UBToolWidget is QWidget now.

Still have some mesh with undo stack and with widget content.

Reworked resizing of items on board. Still have troubles with resizing at BottomRight resizer.

Now 1st added pixmap is selected.
All selected items is deselected after adding any new item.

Document navigator: "Add pages from file" isn't work with old UBZ

Triangle: Resizing of the tool is broken

1st we remove original widget, then we disable undo stack, create a copy of widget and make it a tool. Then undo stack enables back. That widget has tool as parent, so we not need to manage him by scene.